A 32-year-old male from rural Odisha presents with fever, chills, and headache for 3 days. He reports a history of mosquito bites 10 days ago. On examination, he is febrile (38.5°C) with hepatosplenomegaly. A peripheral blood smear taken during a fever spike shows ring-form trophozoites with Schüffner's stippling and occasional infected RBCs containing 2–3 parasites. What is the most likely diagnosis?

Explanation

## Diagnosis: Plasmodium vivax Malaria ### Key Morphological Features on Blood Smear **Key Point:** Schüffner's stippling is pathognomonic for P. vivax and P. ovale; it appears as fine, dust-like dots in the RBC cytoplasm when stained with Romanowsky dyes. **High-Yield:** Multiple parasites per RBC (2–3 in this case) is characteristic of P. vivax; P. falciparum typically shows only 1 parasite per RBC, while P. malariae shows 1 parasite per RBC with coarse stippling (Maurer's clefts). ### Differential Features of Plasmodium Species | Feature | P. vivax | P. falciparum | P. malariae | P. knowlesi | |---------|---------|---------------|-------------|-------------| | **Schüffner's stippling** | Fine, prominent | Absent | Coarse (Maurer's clefts) | Absent | | **Parasites per RBC** | 2–3 (multiple) | 1 (single) | 1 (single) | 1–2 | | **RBC size** | Enlarged | Normal | Enlarged | Normal | | **Fever pattern** | Tertian (48 hrs) | Quotidian (24 hrs) | Quartan (72 hrs) | Quotidian (24 hrs) | | **Gametocyte morphology** | Oval, fills RBC | Crescent-shaped | Round | Round | ### Clinical Correlation **Clinical Pearl:** P. vivax has a predilection for young RBCs (reticulocytes), leading to lower parasitemia (<1%) compared to P. falciparum. This explains why P. vivax is less likely to cause severe malaria, but relapse occurs due to hypnozoites in the liver. **Key Point:** The fever pattern in this patient (fever spike on day 10, suggesting tertian fever) is consistent with P. vivax's 48-hour erythrocytic cycle. ### Why This Patient's Presentation Fits P. vivax 1. **Schüffner's stippling** — diagnostic for P. vivax or P. ovale 2. **Multiple parasites per RBC** — rules out P. falciparum and P. malariae 3. **Hepatosplenomegaly** — common in P. vivax 4. **Fever pattern** — tertian (every 48 hours) is classic for P. vivax [cite:Park 26e Ch 8]